This application claims the priority of International Application No. PCT/JP02/00317, filed Jan. 18, 2002, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a radar that detects the existence of a target by transmitting radio waves and receiving the waves reflected from the target.
Radio radars are employed in a variety of fields for measuring the distance to a target. For example, in the automobile manufacturing industry, development is proceeding on radar for vehicle loading that measures the distance between a forward vehicle and another vehicle.
Such radar are classified into a variety of forms depending on the waveform of the radio waves used. In an article entitled “Current Status and Trends of mm-Wave Automobile Radar”, on pages 977–981 of the October, 1996 edition, Journal of the Institute of Electronic Information and Communication Engineers for example, a variety of forms of radar are mentioned, including pulse radar, FSK (Frequency Shift Keying) CW (Continuous Wave) radar and FMCW (Frequency Modulated Continuous Wave) radar. A pulse radar is a wireless device that emits pulse waves and detects the distance to a target based on the time that elapses until the echo waves are received. The FSK is a wireless device that emits each of two different continuous wave alternatively, based on a Doppler-shift of each echo thereof, and detects the distance to a target object and the relative speed of the target object. An FMCW radar is a wireless device that emits continuous waves of a suitable repeating frequency modulation, such as a triangular wave frequency modulation or the like, and detects the distance to a target object and the relative speed of the target object based on the beat frequency of the transmitted signals and the reflected signals. Among such radar, FSK CW and FMCW radars detect the distance to and relative speed of a target based on the phase and frequency of peak signals of a frequency spectral obtained by FFT (Fast Fourier Transform) processes applied to signals received at a reception antenna.
First, a vehicle mounted radar is mounted on the vehicle mainly for the purpose of detecting a target (such as a vehicle in front) that exists on the surface of the road, therefore the radar may not erroneously detect a pedestrian bridge positioned over the road for example, as the target. Thus, the radar must maintain an attitude when in the condition of being mounted on the vehicle, enabling radio waves to be transmitted to the planar direction of the road surface and radio waves to be received from the planar direction of the road surface. The technology disclosed in JP-A-2000-56020 is well know in connection with such radars. This technology provides two electromagnetic wave emitting sources for emitting electromagnetic waves in slightly vertically inclined directions for the forward direction of a vehicle, mounted on an object detection apparatus, with changes in the attitude of the object detection apparatus being detected by comparing the strength of reflected waves of the electromagnetic waves from each electromagnetic wave emitting source. JP-A-2000-56020 cites laser rays and milliwaves as examples of the electromagnetic waves.